How to Choose the Right Size Dehumidifier

how to calculate dehumidifier capacity and select right size

Dehumidifiers are high-effective units ideal for protecting our homes from moisture damage, mold and mildew growth. However, for a dehumidifier to work properly and help your space, you need to size it right. So, how do you choose the right size dehumidifier?

It all starts by determining the size, humidity, and temperature of the space you want to dehumidify. With these three, choosing the right size dehumidifier becomes easy. The best part is, there is a table here to help you narrow down the sizing further by crossing the damp level with the dehumidifier capacity in pints.

The process of sizing a dehumidifier isn’t complicated. And thanks to this post, you will now know how you can choose the right size dehumidifier for your home. Read it to the end!

How Do You Size a Dehumidifier

Choosing the right size dehumidifier for your home is an important decision. If you’ve never had a dehumidifier before, it can be difficult to know the size you need just by looking at its specs, such as how much power it can offer.

However, if you want to size your dehumidifier right, see below for some tips on choosing the perfect sized unit.

1) How Big is the Area or Room You Want to Dehumidify?

The first thing to look at is the square footage of the area that you are trying to dry out. You can use a tape measure, ruler or a digital laser measure to get this measurement. You need to get the length and width of your space and multiply the two to get the square footage.

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In some cases, you want to measure the walls, ceiling height, and widths to help you get this figure more accurately. Keep in mind some rooms, especially the basements, typically have odd shapes rather than standard square areas.

Remember, you will need this information to determine the capacity of your ideal dehumidifier in pints.

You can get a normal movable dehumidifier for your space but to a certain size. If the area is larger than 2,500 square feet, it’d be best to get a whole-house dehumidifier. It’s also an excellent choice if you need to dehumidifier the entire house.

The best part is, even though the installation is done by a professional, you can get one that hooks up to your pre-existing central heating system or the air vent system.

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2) Examine the humidity levels in your home

This can be measured using a humidity gauge – you can get one at any hardware store. Some experts recommend putting it up in your basement for around 30 days to see the average level. If you have some dampness that you are trying to remedy immediately, use this figure instead of averaging over time.

A home or building should have about 40-60% humidity. A basement, especially one with flooding problems, might need to be as low as 30%. Otherwise, it is better to be between 40 and 60% to avoid moisture damage.

The ideal place to use a dehumidifier is in basements or other spaces that tend to get damp because they sit at lower levels than the rest of the house (basement, crawl space). A thermostat can give you correct humidity levels in those areas.

Humidity Level (%)Environment ConditionHow it feels
50-60Moderately DampThe air feels damp, heavy, or clammy – you can start to notice must odor
60-70Very DampThe space feels damp and smells musty – you can start to notice damp spots on the walls and floor
70-80WetThe water beads on the floors and walls or seeps in around the room edges – the area feels and smells damp
80-100Extremely WetThere is standing water on the floor.

3) How Many Pints of Water Per Day Will the Unit Remove?

Dehumidifiers are sized in pints of water they can remove in a given period. You want to get one that removes enough for your home size. By looking at their specs, most units will let you know the amount of pints/day they can handle. It’s also written under them if you’re having trouble finding it. You can use the AHAM Dehumidifier Sizing Chart below.

Size of the Area to be Dehumidified (sq. ft.)

Humidity Levels (%)300 sq.ft. 500 sq. ft.800 sq. ft.1200 sq. ft.
Slightly Damp Air
20-pint 30-pint40-pint50-pint
Heavier Air & Musty Smell
Water Beads on Floor and Walls
Standing Water on the Floor

4) The Temperature of the Environment

This is one of the most important factors in deciding the size. Cold air holds less moisture than warm air, so if you are trying to dehumidify a cold area, you’ll be able to remove more moisture from that space with a smaller unit.

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On the other hand, if it’s very warm outside but cool inside your home, you may need a larger unit to compensate for the generated heat. You can install a thermostat, which will measure how much humidity is in the room and the temperature levels.

Another thing, dehumidifiers are designed to work at various temperatures. And if you don’t know it yet, dehumidifiers are of two basic types: refrigerant and desiccant refrigeration. Which one you should use is determined by a few factors, one of them being the temperature.

Desiccant dehumidifierIf the temperature in the space you want to dry falls under 18°C (65°F), get a desiccant dehumidifier. These units are resistant to freezing since they use water-absorbing material such as silica gel that helps draw out the moisture for the air. They operate quietly and are preferable for cooler spaces; however, most residential desiccant dehumidifiers use single-use cartridges and are generally expensive to run.
Refrigerant dehumidifierIf your space is hot and humid constantly, a refrigerant dehumidifier is your best choice. These models have higher capacity ratings, and they are effective at high temperatures compared to their counterparts. They use a heat exchange coil to extract water from the air. You can either use a portable unit or a whole-house model. If the room temperature was to go below 18°C (65°F), ice could form on the evaporator coils and reduce its effectiveness.

5) What Features are Included?

Also, pay attention to the features that come with each unit, like auto-defrost and electronic controls. These can make a dehumidifier more cost-effective by reducing energy use and ensuring that it does its job properly, even when needed most.

The physical size, though, might increase depending on what features are included. So, you might want to check the dimensions and compare them with your available placement space.

6) How Much Maintenance You Handle

What parts of the dehumidifier can be taken apart and cleaned? This is often something that needs to be done every season or yearly, depending on how much dampness comes through in your area. You want to make sure you can handle the dehumidifier size you’re about to purchase.

Besides, will you be able to empty the bucket frequently? If not, a model with a sizeable bucket is the best option as it’ll allow less draining, but the maintenance might be high.

7) Price

This isn’t always a huge factor when deciding on what’s right for your home, but you may want to consider what quality of the product you get with the price you pay. Cheaper units may have less power or no auto defrost feature. Of course, don’t forget to add in more money if you’ll need to hire a professional to install it.

Dehumidifier Sizing Standards

Dehumidifier sizing standards vary widely depending on the manufacturer. The production company offers two types of dehumidifiers with normal and high standards. These are not standardized by any standardization institution, so it is best to determine the required size based on relative humidity’s total area.

The size of a dehumidifier for a small room can be calculated using this formula: X ÷ 800 = m³/d (m ³/day) where X = area in square meters, Y = Relative Humidity, m = Max Dehumidification Capacity (L per day).

The results will give an approximate value of the amount of time spent running at full capacity. It is necessary to multiply capacity times by the number of hours to cover the space. Therefore, if a capacity of 600L/day and relative humidity of 60%, it means that 15 L / day is enough for one room.

To prevent condensation from occurring inside the appliance, one should always have at least 1 liter per square meter of surface area where evaporation can release moisture.

In addition, remember that as time passes will begin to “dilute” the extracted water, so the need for greater extraction ability is gradually reduced over time. However, we must not forget to occasionally check and replace the water in coolers (humidity).

Suppose you want to purchase a large dehumidifier: Y = Relative Humidity (%). The amount of time spent running at full capacity can be calculated with this formula: X ÷ 1000 = m³/d (m ³/day).

If, instead, having a high humidity in several areas or buildings to consider the purchase of several appliances. If an area has an average relative humidity of 60%, round up the square meters, so it’d need 6 square meters per appliance.

The calculation is similar to the previous one, but you have to calculate the total square meters and divide by 800. So if we had 20 square meters, it would need (20×800) ÷ 800) 1600 Liters/day divided by 8 hours, that is 200 liters consumed per hour; then multiplied by 24 hours, which is 4,800 liters per day.

If the area has an average relative humidity of 80%, you would need (20×800) ÷ 800 = 2400 L/day divided by 8 = 300 Liters consumed per hour; multiplied by 24 hours, that’s 7200 Liters per day. This amount should be enough to move two appliances running simultaneously for around 10 hours; if not, it is recommended to use refrigerant dehumidifiers or large capacity.

Summary: Ultimately, the purchase decision comes down to you. Many things can affect it and change how you think about any given model. The most important thing is to buy something that will help get rid of dampness in your basement, but there are other factors you should consider as well.

Related Questions

Can you use a large dehumidifier in a small room?

Yes! The dehumidifier operates depending on the settings you have keyed in on its thermostat. So, even if it’s a huge model and you’ve set the humidity level to 30-50%, the dehumidifier will strip the moisture from the air up to this point, no matter the size. The benefit of oversizing is, the unit will be faster and will require less frequent maintenance. However, it might cost you extra. But as always, it’s better to go big than go small.

About the author

Sharif Hasan

I am Sharif a data-driven marketer by profession and run The Spruce Air. I am very interested in keeping good-quality air inside of my home. Besides, I love to share my air-related knowledge through my website.

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